1. Field of the Invention
The present invention relates to a single cylinder engine with a ternary catalyst in an exhaust passage, and a vehicle provided with the same.
2. Description of the Related Art
Conventionally, a catalyst capable of purifying CO, HC and NOx at the same time, that is, a ternary catalyst, is used to purify exhaust gases from an engine (for example, see JP-A-2004-150310, paragraph 0040). In order to have an effective ternary catalyst, it is necessary to perform combustion in an engine at a theoretical air fuel ratio.
In recent years, a further improvement in economy in fuel consumption for engines has been desired. As one of the measures for improving fuel economy, it is conceivable to reduce fuel consumption at the time of decelerated operation by making an air-fuel ratio larger at the time of decelerated operation than at the time of steady speed. For example, in engines in which combustion at a theoretical air fuel ratio is performed at the time of steady speed, it is conceivable to make an air-fuel ratio larger at the time of decelerated operation than a theoretical air fuel ratio. However, when an air-fuel ratio deviates from a theoretical air fuel ratio it is not possible to have an effective ternary catalyst, so that favorable purification of exhaust gases becomes difficult. Therefore, it is difficult to make a further improvement fuel consumption economy compatible with purification of exhaust gases by a ternary catalyst.